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Authorised and issued share capital - Options Granted, WPP Executive Share Option Scheme (Detail) - Ordinary shares [member]
 12 Months Ended
Dec. 31, 2018
GBP (£)
shares
Dec. 31, 2017
Disclosure of range of exercise prices of outstanding share options [line items]    
Number of ordinary shares under option 24,218,615 20,985,441
WPP Executive Share Option Scheme [member]    
Disclosure of range of exercise prices of outstanding share options [line items]    
Number of ordinary shares under option 6,741 6,741
WPP Executive Share Option Scheme [member] | Exercise price group 1 [member]    
Disclosure of range of exercise prices of outstanding share options [line items]    
Number of ordinary shares under option | shares 3,696  
Exercise price per share | £ £ 8.333  
Exercise dates 2015 - 2022  
WPP Executive Share Option Scheme [member] | Exercise price group 2 [member]    
Disclosure of range of exercise prices of outstanding share options [line items]    
Number of ordinary shares under option | shares 3,045  
Exercise price per share | £ £ 10.595  
Exercise dates 2016 - 2023